Electrode for High Performance Metal Halogen Flow Battery

Abstract

A porous electrode for a flow battery includes a first layer and a second layer. The first layer has at least one of a different catalytic property or a different permeability than the second layer.

What is claimed is: 
     
         1 . A porous electrode for a flow battery comprising a first layer and a second layer, wherein the first layer has at least one of a different catalytic property or a different permeability than the second layer. 
     
     
         2 . The electrode of  claim 1 , wherein the first layer has a lower catalytic property than the second layer. 
     
     
         3 . The electrode of  claim 2 , wherein the second layer comprises at least one of sintered metal oxide powder which catalyzes oxidation of a metal-halide electrolyte to form halogen ions, or a sintered metal or metal oxide powder which is coated with a mixed metal oxide catalytic coating which catalyzes oxidation of the metal-halide electrolyte to form the halogen ions. 
     
     
         4 . The electrode of  claim 3 , wherein the first layer comprises at least one of a porous metal foam, a porous metal oxide foam, or a porous sintered metal or metal oxide powder, and wherein the first layer is thicker than the second layer. 
     
     
         5 . The electrode of  claim 4 , wherein the first layer comprises a sintered first powder having a first size distribution and the second layer comprises a sintered second powder having a second size distribution which is tighter than the first size distribution. 
     
     
         6 . The electrode of  claim 5 , wherein:
 the first powder comprises titanium metal, tungsten metal, tantalum metal, titanium oxide, tantalum oxide, tungsten oxide or combinations thereof; and   the second powder comprises titanium metal, tungsten metal, tantalum metal, titanium oxide, tantalum oxide, tungsten oxide, or combinations thereof coated with the catalytic coating of ruthenium oxide and titanium oxide.   
     
     
         7 . The electrode of  claim 6 , wherein the second layer is coated on the first layer. 
     
     
         8 . The electrode of  claim 2 , wherein the second layer has a BET surface between 0.001 and 0.5 m 2 /g. 
     
     
         9 . The electrode of  claim 2 , wherein the first layer comprises a sintered metal or metal oxide powder substrate layer and the second layer comprises a mixed metal oxide catalytic coating which is coated onto a portion of the substrate layer. 
     
     
         10 . The electrode of  claim 9 , wherein first layer comprises a sintered titanium powder substrate layer and the second layer comprises a 100 to 500 nm thick mixed ruthenium oxide and titanium oxide coating which extends into the first substrate layer to a penetration depth between 0.1 and 1 mm. 
     
     
         11 . A metal halogen flow cell comprising a positive electrode comprising the electrode of  claim 1  and a negative electrode separated from the positive electrode by a separator free reaction zone, wherein the second layer faces the negative electrode and the reaction zone of the flow cell. 
     
     
         12 . The metal halogen flow cell of  claim 11 , further comprising an electrically insulating porous restriction layer located between the positive electrode and negative electrode of an adjacent flow cell. 
     
     
         13 . The metal halogen flow cell of  claim 12 , wherein the restriction layer comprises a porous plastic layer which is located in contact with the second layer of the positive electrode. 
     
     
         14 . The metal halogen flow cell of  claim 13 , wherein:
 the positive electrode and the negative electrode are supported by a stack of insulating cell frames;   the positive electrode is supported in the reaction zone by one or more insulating spacer ribs;   the one or more spacer ribs divide an active area opening in each cell frame into a plurality of flow areas;   each of the plurality of the flow areas is between 200 mm and 1000 mm long and between 50 to 150 mm wide;   a gas permeability of the porous restriction layer is between 1×10 −10  and 5×10 −6  cm 2 ;   an in-plane resistance of the positive electrode per centimeter width and centimeter depth is between 2×10 −4  and 5×10 −1  ohms; and   a flexural modulus times thickness cubed parameter of a combination of the positive electrode and the porous restriction layer is between 0.1 and 1200 Newton-meters.   
     
     
         15 . An electrochemical flow battery comprising a plurality of flow cells of  claim 11 , an electrolyte reservoir and an electrolyte pump. 
     
     
         16 . The electrode of  claim 2 , wherein the first layer has a higher permeability, a lower permeability or substantially the same permeability as the second layer. 
     
     
         17 . The electrode of  claim 1 , wherein the first layer has a higher permeability or a lower permeability than the second layer. 
     
     
         18 . A method of making a porous electrode for a flow battery, comprising:
 providing a first substrate layer comprising a sintered metal or metal oxide powder substrate layer; and   coating a portion of the first substrate layer with a mixed metal oxide catalytic coating.   
     
     
         19 . The method of  claim 18 , wherein first substrate layer comprises a sintered titanium powder substrate layer and the second layer comprises a 100 to 500 nm thick mixed ruthenium oxide and titanium oxide coating which extends into the first substrate layer to a penetration depth between 0.1 and 1 mm. 
     
     
         20 . The method of  claim 19 , wherein the step of coating comprises coating a mix of a solid catalyst phase and a liquid carrier phase on the first substrate layer. 
     
     
         21 . The method of  claim 20 , wherein the mix comprises a colloid or suspension of solid ruthenium oxide and titanium oxide in an organic liquid which evaporates before penetrating an entire thickness of the first substrate layer after the step of coating to achieve the mixed ruthenium oxide and titanium oxide coating penetration depth of between 0.1 and 1 mm into the first substrate layer. 
     
     
         22 . A method of making an electrochemical flow cell, comprising:
 providing a positive electrode made by the method of  claim 18 ;   providing a negative electrode spaced apart from the positive electrode by a reaction zone, such that the positive electrode so that the second layer faces the negative electrode and the reaction zone.   
     
     
         23 . The method of  claim 21 , further comprising providing an insulating porous restriction layer located between the positive electrode and a negative electrode of an adjacent flow cell.